240 



s. GOTO 



to allow the larvae to float, and the mixture then poured in. The larvae 

 were left in it for 3-5 minutes, then passed through the ascendino- 

 grades of alcohol, beginning with al)out 30%, and finally preserved in 

 10% alcohol, in wdiich the remaining sublimate was thoroughly washed 

 out with iodine. The result was very satisfixctory, except that, as I 

 had noticed while in Newport, the volume of the larvie was perceptibly 

 diminished, when they were left too long in the mixture, evidently 

 owing to osmotic pressure. To prevent this when I was working with 

 the eggs of the sea-urchin last winter I diluted the above mixture with 

 distilled water to the specific gravity of sea- water, viz. to 2^j^ times 

 the original volume roughly. This dihited mixture I can recommend 

 as excellent for many dehcate pelagic larvœ (îinnelid larvœ, mitraria, 

 ephyra, small hydromedusœ, etc.). 



The general featnres of tlie development of the present species are 

 well known from the excellent p:iper of A. Agassiz ['77] ; I have 

 therefore only drawn, in Plate XIX, the principal stages that come 

 into consideration in this paper, beginning with a fully developed 

 bipinnaria and reaching up \o a young star, in which the permanent 

 mouth is being developed. These stages, seven in all, will be referred 

 to in the order of their age by the letters of the alpliabet (Pi. XIX). 



I. General Form of the Body. 



Externally the bipinnaria is distinguished by its perfect bilateral 

 symmetry, and no one has, so far as I know, succeeded in establishing 

 a genetic relation between the principal plane of this bilateral symmetry 

 and the axis of the radial symmetry that preponderates later. For 

 ■example, one of the latest students of echinoderni morphology has observ- 

 ed that " le plan de symétrie bilatérale acquis secondairement ou déter- 

 miné par l'existence d'organes impairs, n'a aucun rapport avec le plan de 



